In thread processing machines, particularly two-for-one twisters, the thread coming from the processing or twisting spindle assembly ordinarily has a very high tension which adversely affects winding of the processed thread at the take-up mechanism. Accordingly, a driven pre-take-up roller mechanism is often arranged between the thread processing spindle assembly and the take-up mechanism to overfeed the thread and reduce the thread tension.
Conventionally, the pre-take-up rollers are positively driven by a drive shaft carried by the thread processing machine in such a way that the circumferential speed thereof at the surface in contact with the thread is distinctively higher than the speed of travel of the running thread so that the running thread is subjected to a variation of its tension due to the relative speed between the pre-take-up roller and the running thread. When the circumferential speed of the pre-take-up roller is higher than the running speed of the thread, which is determined by the winding speed of the take-up mechanism, the thread tension after the pre-take-up roller is less than the thread tension before the pre-take-up roller which is desirable for effective operation of the take-up mechanism. Also, this variation in tension could be easily adjusted for various types of threads by adjustment of the rotational speed of the drive shaft.
However, since the running thread is in frictional engagement with the pre-take-up roller, the running thread is inherently subjected to undesirable frictional wear with this type of arrangement. Delicate and high quality threads, e.g. smooth filament yarns or sewing threads, are considerably damaged with the use of these conventional pre-take-up roller mechanisms at normal production rates. Such threads, therefore, must be processed at reduced production rates with a resulting, greatly reduced production capacity, in order that the thread tension prior to the pre-take-up roller is lower and does not require a great amount of additional further reduction in tension at the pre-take-up roller mechanism.
Conventional pre-take-up rollers normally utilize a ball-like structurized shape having a running groove therein in which the surface of the roller in direct contact with the running thread is either hard chromium plated or is provided with a plasma layer, such as oxide material. The degree of roughness of the surfaces of direct contact with the thread is limited. Notwithstanding, the above described problem with frictional wear by the conventional direct driven pre-take-up rollers still exist.
An example of such positively driven pre-take-up roller mechanism in a thread processing machine is disclosed in prior art U.S. Pat. No. 4,346,551.